Advantech SOM-ETX Design Guide
5.9.2 Design Note
All COM Port transmitters are added on the carrier board. For designing the function
of wake on Modem you must diode-OR the RI# signal to the connector X4-D26
“RINGWAKE#”.
Figure 5-28 Serial Bus Connections
Figure 5-29 Serial Bus Layout Guidelines
2. Pull-up resisters are needed for unused input COM ports signals(DSR#,
CTS#, RI#, DCD#). Here is an example for your reference:
5.10 LPT/Floppy
Notes:
1. The signals TXD, DTR #, RTS# are normally outputs, but are also used as
straps during the system reset. No external pull-ups or pull downs needed
on these lines, which may affect the system configurations.
Ex: use TXD and RXD only
SOM-ETX generally supports either one parallel port or one Floppy drive. While the
parallel port is used in parallel port mode, floppy disk support is not available via the
parallel port. If both floppy drive and parallel port are needed, an external controller
may be incorporated in the baseboard design
SOM-ETX
RTS#1
Com port
D-Sub 9
DTR#1
TXD1
RXD1
CTS#1
DCD#1
RI#1
DSR#1
Transmitter/
Reciver
1
9
8
7
6
4
3
2
5.9.3 Layout Requirement
Sometimes in order to avoid EMI issue, we often separate ground to frame
ground(I/O ground). Adding bead and capacitor to baseboard is necessary.
frame ground
SOM-ETX
RTS#1
Com port
DTR#1
TXD1
RXD1
CTS#1
DCD#1
RI#1
DSR#1
Transmitter/
Reciver
D-Sub 9
1
9
8
7
6
4
3
2
5
bead
bead
bead
bead
bead
bead
bead
bead
180p
Chapter 5 Carrier Board Design Guidelines
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